LC oscillator

ABSTRACT

An LC oscillator capable of oscillating even if it is fabricated on a substrate comprises a transistor, capacitor, and an inductor element  30 . The inductor element  30  has two spiral conductors  120, 122  having substantially the same shape and formed on a semiconductor substrate  110 . The inner end of the conductor  120  is electrically connected to the outer end of the conductor  122 . Lead wires  130, 132  are connected to the outer and inner ends of the conductor  120  respectively. The lead wire  132  is passed through the lower conductor  122  and the semiconductor substrate  110  and led outside. The upper A conductor  120  serves as an inductor conductor and is connected to another component of the LC oscillator formed on the semiconductor substrate  110  through the lead wires  130, 132.

TECHNICAL FIELD

The present invention relates to an LC oscillator that can be formed onvarious kinds of substrates such as a semiconductor substrate.

BACKGROUND ART

There is known such a semiconductor circuit that forms a spiral patternelectrode on a semiconductor substrate by using thin film formingtechnique, and uses this pattern electrode as an inductor element. Whencurrent flows in such an inductor element that is formed on asemiconductor substrate, magnetic flux is generated in the directionperpendicular to a spiral pattern electrode. Nevertheless, since eddycurrents are induced on the front side of the semiconductor substrate bythis magnetic flux to cancel effective magnetic flux, there is such aproblem that doesn't effectively function as the inductor element. Inparticular, since the higher a frequency of a signal which flows in theinductor element becomes, the more remarkable this inclination becomes,and consequently it is difficult to form an LC oscillator, including theinductor element as a resonance element, on a semiconductor substrate.

DISCLOSURE OF THE INVENTION

The present invention is achieved in view of such a point. Its object isto provide an LC oscillator that can perform oscillation even if the LCoscillator is formed on a substrate.

An inductor element included in an LC oscillator of the presentinvention has two conductors that are formed in piles on a substrate inthe state where they are mutually insulated, and are connected with eachother at both odd ends. While one conductor separating from thesubstrate is used as an inductor conductor, a lead wire of this inductorconductor is led out through a gap between another conductor, being nearthe substrate, and the substrate. It is experimentally confirmed that aninductor element that has such structure has predetermined inductancewithout losing an inductance component by eddy currents etc. even if theinductor element is formed on a substrate. With using this inductorelement as a part of an LC oscillator, oscillation can be performed evenif the LC oscillator is formed on the substrate. In particular, byleading out the lead wire of this inductor conductor included in theinductor element from between another conductor and the substrate, itbecomes possible to preventing the flow of the effective magnetic flux,generated by the inductor conductor, to the minimum from beinginterrupted. Hence good characteristics can be obtained.

In case where the inductor element described above has three or morelayers of metal layers formed on the substrate, it is desirable to formthe two conductors described above and lead wires respectively withusing different metal layers which are mutually apart by one or morelayers. Since the inductor conductor can be made to be apart from thelead wires by at least two or more layers by adopting such constitutionof the inductor element included in the LC oscillator, it is possible tofurther reduce the influence of the electric current that flows in thelead wires.

In addition, it is desirable to connect the two conductors included inthe inductor element mentioned above at both odd ends with using a partof a lead wire of the inductor conductor extending from the one end ofthe inductor conductor. Since the number of the conducting wires (leadwires and connecting wires) that intersect the inductor conductor can bereduced, a degree of interrupting the flow of the effective magneticflux generated by the inductor conductor can be further reduced. Inaddition, since the shape of a mask can be simplified when manufacturingeach conductor and lead wires with using an aligner etc., it is possibleto reduce a cost and labor hours for manufacturing the whole of the LCoscillator.

Furthermore, an inductor element included in the LC oscillator of thepresent invention has two conductors that are formed in piles on asubstrate in the state where they are mutually insulated, and areconnected with each other at both odd ends. While using one conductorapart from the substrate as an inductor conductor, one end of anotherconductor not connected to the inductor conductor is terminated with apredetermined impedance element. Although electric current flows also inanother conductor by the effective magnetic flux generated by theinductor conductor in the inductor element, it becomes possible toprevent unnecessary reflection in this portion and to improvecharacteristics of the inductor element by terminating the end of thefree side of another conductor with the impedance element. Hence,oscillation can be performed reliably by the LC oscillator comprisingthe inductor element. In addition, it is possible to adjust frequencycharacteristics or the like of another conductor by forming theimpedance element described above with using any of a resistor, acapacitor, and an inductor or combining these. Hence it becomes possiblealso to adjust oscillation characteristics finely by adjusting a deviceconstant of the impedance element at a suitable value.

In addition, it is desirable to adjust termination conditions by makingit possible to change at least one device constant of a resistor, acapacitor, and an inductor, which constitute the impedance elementdescribed above, and making this device constant variable. By someexternal means, for example, by changing a value of a control voltageapplied, it becomes possible to adjust a device constant of the wholeimpedance element, that is, characteristics of the inductor element by achange of termination conditions. It also becomes possible to adjustfinely an oscillation frequency.

In particular, when the substrate described above is a semiconductorsubstrate, it is desirable to form the capacitor where a device constantcan be changed by a variable capacitance diode. While it becomespossible to miniaturize parts by using the variable capacitance diodeformed with using the semiconductor substrate, it becomes possible toreduce a cost for manufacturing LC oscillator by simplifyingmanufacturing process in comparison with the case where external partsare attached thereafter, and wiring etc. are performed. Similarly, whenthe substrate described above is a semiconductor substrate, it isdesirable to form a variable resister made of an FET whose channel isused as a resistor. While it is possible to miniaturize parts by usingthe variable resistor made of the FET formed with using thesemiconductor substrate, it becomes possible to reduce a cost formanufacturing LC oscillator by simplifying manufacturing process incomparison with the case where external parts are attached thereafter,and wiring etc. are performed.

In addition, it is desirable to form an inductor, which constitutes theimpedance element, by a conductive layer formed on the substrate inpredetermined shape. Since high Q is not required of the inductor usedfor terminating one end of a conductor, it is possible to realize theinductor with a conductor pattern on the substrate. Moreover, since itbecomes possible to form this conductor pattern at the same process withusing a metal layer for performing various kinds of wiring etc., itbecomes possible to perform miniaturization of entire LC oscillator,simplification of process, and cost reduction.

In addition, as a substrate mentioned above, it is preferable to use asemiconductor substrate, and to form each configuration parts of LCoscillator on the substrate. If the inductor element that effectivelyfunctions can be formed on a semiconductor substrate, it is possible toform each configuration parts for LC oscillator, including the inductorelement, on the semiconductor substrate. Hence it becomes possible toform the whole of the LC oscillator on the semiconductor substratewithout using any external parts.

In addition, it is desirable to form two conductors, described above, inthe substantially same shape or long shape. Since an upper conductornever directly faces the front side of the substrate owing to making thetwo conductors the same in shapes, it is possible to reduce the eddycurrents that are generated on the substrate when the upper conductordirectly faces the substrate. In addition, it is possible to givepredetermined inductance to the upper conductor by making the shapes ofthe two conductors be long. In particular, since it is possible to givelarge inductance to a conductor when the conductor is formed in one ormore turns of spiral shape or a meander shape, the conductor is suitablefor being built in an LC oscillator having comparatively low frequency.In addition, since it is possible to give a small inductance to aconductor when the conductor is formed in a circular shape less than oneturn or an substantially linear shape in comparison with the case wherethe conductor is formed in a spiral shape or the like, the conductor issuitable for being built in an LC oscillator having comparatively highfrequency.

Moreover, when two conductors are made in spiral shapes, it ispreferable to connect an inner end of one conductor with an outer end ofanother conductor. Since it is experimentally confirmed that it ispossible to secure further large inductance when an inductor conductoris formed on a substrate owing to performing such connection, it ispossible to realize the inductor element that effectively functions on asubstrate. In particular, when the shape is a spiral one having one ormore turns, it is necessary to extend a lead wire from the innercircumferential end of the inductor conductor having this spiral shape.Nevertheless, it is possible to suppress to the minimum the interruptionof flow of the effective magnetic flux, generated by the inductorconductor, by leading out the lead wire between the conductor, beingnear the substrate, and the substrate.

In addition, the inductor element described above is suitable for use asa compound element that also has a capacitance component besides aninductance component. Since this inductor element has two conductors,mutually superimposed, and a capacitance component is also included inits characteristics, the characteristics of this inductor element can beeffectively used by using this inductor element as one part of the LCoscillator where an inductor and a capacitor are used in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a configuration of an LC oscillatoraccording to a first embodiment;

FIG. 2 is a schematic diagram showing a planar structure of an inductorelement included in the LC oscillator shown in FIG. 1;

FIG. 3 is a drawing showing an upper layer of conductor included in theinductor element shown in FIG. 2;

FIG. 4 is a drawing showing a shape of a lower layer of conductorincluded in the inductor element shown in FIG. 2;

FIG. 5 is a schematic diagram showing a connection state of twoconductors included in an inductor conductor;

FIG. 6 is an enlarged sectional view taken on line VI—VI in FIG. 2;

FIG. 7 is a chart showing measurement result of an output characteristicof an LC oscillator;

FIG. 8 is a chart showing measurement result of an output characteristicof an LC oscillator;

FIG. 9 is a chart showing measurement result of an output characteristicof an LC oscillator;

FIG. 10 is a chart showing measurement result of an outputcharacteristic of an LC oscillator;

FIG. 11 is a schematic diagram showing a structure of an inductorelement according to a second embodiment;

FIG. 12 is a drawing showing the structure in the case of connecting avariable capacitance diode to the inner circumferential end of a lowerlayer of conductor;

FIG. 13 is a drawing showing the cross-sectional structure in the caseof forming the variable capacitance diode, shown in FIG. 12, on asemiconductor substrate;

FIG. 14 is a diagram showing the structure in the case of connecting avariable resistor to the inner circumferential end of a lower layer ofconductor;

FIG. 15 is a chart showing measurement result of an outputcharacteristic of an LC oscillator;

FIG. 16 is a chart showing measurement result of an outputcharacteristic of an LC oscillator;

FIGS. 17A through 17C are schematic diagrams showing modified examplesof the conductors included in the inductor elements; and

FIG. 18 is a drawing showing a modified example of the inductor element,the drawing where a connecting wire that connects ends of two conductorsis omitted.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, an LC oscillator according to an embodiment where the presentinvention is applied will be specifically described with referring todrawings.

First Embodiment

FIG. 1 is a circuit diagram showing a configuration of an LC oscillatoraccording to the first embodiment. An LC oscillator 10 shown in FIG. 1has a transistor 20, a capacitor 22 connected between the base and theemitter of the transistor 20, a capacitor 24 connected between theemitter and the collector of the transistor 20, a capacitor 26 connectedserially between the base and the collector of the transistor 20 and aninductor element 30.

In this LC oscillator 10, the capacitance of two capacitors 22 and 24maybe several tens times the between-terminal capacity of a transistor20. In addition, an inductor element 30 is connected through a capacitor26.

An LC oscillator 10 having the configuration described above in thisembodiment is a Clapp circuit that is an advanced Colpitts circuit. Inthe LC oscillator 10, a capacitor of a resonant circuit that determinesan oscillation frequency becomes equivalent to series connection ofcapacitors 22, 24, and 26. Hence, it is possible to select largercapacitance of capacitors 22 and 24 than that of the Colpitts circuitthat does not have a capacitor equivalent to the capacitor 26.Therefore, even if the capacitance between terminals of a transistor 20changes, it does not give large influence to the resonant frequency of aresonant circuit, and hence it is possible to improve the stability ofthe oscillation frequency.

FIG. 2 is a schematic diagram showing a planar structure of an inductorelement 30 included in the LC oscillator 10 according to thisembodiment. In addition, FIG. 3 is a drawing showing an upper layer ofconductor included in the inductor element 30 shown in FIG. 2. FIG. 4 isa drawing showing a shape of a lower layer of conductor included in theinductor element 30 shown in FIG. 2.

An inductor element 30 according to this embodiment has two conductors120 and 122 that have spiral shapes and are formed on the surface of asemiconductor substrate 110. These two conductors 120 and 122 havesubstantially the same shape. When viewed from the front side of thesemiconductor substrate 110, they are formed so that the conductor 120,which becomes an upper layer, and another conductor 122, which becomes alower layer, are formed by being superimposed one on the othersubstantially exactly. Each of the conductors 120 and 122 is formed of,for examples, a thin film of metal (metal layer), or semiconductormaterial such as poly silicon.

FIG. 5 is a schematic diagram showing a connection state of the twoconductors 120 and 122, described above. As shown in FIG. 5, lead wires130 and 132 are connected to an outer end (outer circumferential end)and an inner end (inner circumferential end) of the upper conductor 120respectively, and the inner end of the upper conductor 120 and the outerend of the lower conductor 122 are connected with a connecting wire 134.

The upper conductor 120 functions as an inductor conductor, and isconnected to other configuration parts formed on the semiconductorsubstrate 110 through the lead wires 130 and 132 connected to endsthereof.

FIG. 6 is an enlarged sectional view taken on line VI—VI in FIG. 2. Asshown in FIGS. 5 and 6, at least three layers of metal layers 160, 162,and 164 are formed on the surface of the semiconductor substrate 110.One conductor 120 as an inductor conductor is formed with using a toplayer of metal layer 160 that is most apart from the semiconductorsubstrate 110, and another conductor 122 is formed with using a middlelayer of metal layer 162.

In addition, the lead wire 132 led out from the inner circumferentialend of the top layer of conductor 120 is formed with using a bottomlayer of metal layer 164 nearest to the semiconductor substrate 110. Forexample, as shown in FIG. 6, the inner circumferential end of theconductor 120 and one end of the lead wire 132 are connected through athrough hole 150. The lead wire 132 formed from the bottom layer ofmetal layer 164 is led out outward so that the lead wire 132 may beorthogonal to each circumferential portion of the inductor conductorwith a spiral shape. In addition, insulating layers 140, 142, and 144are formed between the conductors 120 and 122, and the lead wire 132,which are formed with using three metal layers 160, 162, and 164, andthe semiconductor substrate 110 respectively, and mutual insulation isperformed.

An inductor element 30 in this embodiment has the structure describedabove. Since predetermined inductance appears between the lead wires 130and 132 connected to both ends of the upper layer of conductor 120respectively, this upper conductor 120 can be used as an inductorconductor. In addition, under this upper conductor 120, the conductor122 that has substantially the same shape as this conductor 120 isformed. It is possible to suppress the generation of eddy currents inthe front side of the semiconductor substrate 110 when an upperconductor 120 is used as an inductor conductor, by connecting one end ofthe upper conductor 120 with one end of the lower conductor 122 with theconnecting wire 134. Hence it is possible to make the upper conductor120 effectively function as an inductor conductor.

Furthermore, in the inductor element 30 in this embodiment, the leadwire 132 led out from the inner circumferential end of the upper layerof conductor 120 serving as an inductor conductor is formed with usingthe bottom layer of metal layer 164, and is located with being mostapart from the inductor conductor through the other conductor 122. Henceit is possible to suppress to the minimum interruption of flow of theeffective magnetic flux generated by the inductor conductor, and toobtain good characteristics. In this manner, the inductor element 30included in the LC oscillator 10 in this embodiment can be formed withusing at least three layers of metal layers 160, 162, and 164 on thesurface of the semiconductor substrate 110. Hence it becomes possible torealize forming the inductor element 30 with other parts in one piece toperform integration on the semiconductor substrate 110.

By the way, the present applicant performed various kinds of experimentsabout the effectiveness of LC oscillator that an inductor element formedby locating the two conductors 120 and 122 is applied, described above,in piles on a substrate and mutually connecting both odd ends. Then, thepresent applicant has already applied for a patent on the basis of theexperimental result (Japanese Patent Application No. H10-140541). The LCoscillator 10 in this embodiment is an advanced one, and is intended toimprove characteristics of inductor element 30 used for the LCoscillator 10 by devising a leading-out position of the lead wire 132with using that the two conductors 120 and 122 have two layer structure.For example, supposing that an inductor conductor with a spiral shape issimply formed on a semiconductor substrate or another substrate, even ifa lead wire is formed with using an upper layer or a lower layer ofmetal layer which is adjacent to a metal layer in which this inductorconductor is formed, it is the same that the inductor layer and the leadwire are closely located. Hence the lead wire interrupts the effectivemagnetic flux generated by the inductor conductor. However, in theinductor element 30 included in the LC oscillator 10 in this embodiment,another conductor 122 is located between one conductor 120, serving asan inductor conductor, and the lead wire 132. Hence it is possible toreduce the turbulence of the effective magnetic flux at the time ofleading out the lead wire 132 so that the lead wire 132 may intersectthe inductor conductor 120.

Hereafter, the effectiveness of the LC oscillator in this embodimentwill be described with reference to the experimental result shown in theapplication described above (Japanese Patent Application No.H10-140541).

FIG. 7 is a graph showing the measurement result of the outputcharacteristics of an LC oscillator configured with an inductor elementwhich has an electrode of one layer having the same shape as theconductor 120 included in the inductor element 30. As for the inductorelement used in this measurement of the output characteristics, afive-turn electrode having one-mm pattern width and a 0.2-mm adjacentgap of spiral pattern was formed on a front side of a 0.13-mm-thickinsulating member with a dielectric constant of 3.17. In addition,vertical axes in FIG. 7 (this is the same also in FIGS. 9 and 10 whichare described later) denote output amplitudes logarithmically expressed,and horizontal axes denote the frequencies of output signalslogarithmically expressed, respectively. As shown in FIG. 7, anoscillation frequency of 119 MHz was observed when the LC oscillatorperforms in the state with sufficiently separating the inductor elementincluding such an electrode of one layer from other conductor substrateor semiconductor substrate.

FIG. 8 is a graph showing the output characteristic of an LC oscillatorat the time of gradually bringing a copper plate, which is a conductivesubstrate, close to the inductor element used for the measurement of theoutput characteristics shown in FIG. 7. Vertical axes in FIG. 8 denoteoutput amplitudes logarithmically expressed, and horizontal axes denotethe frequencies of output signals, respectively. As shown in FIG. 8, itwas observed that, when the copper plate was gradually brought close tothis inductor element in the state of oscillation with using theinductor element comprising one layer of electrode, the oscillationfrequency became higher from 118 MHz to 139 MHz, 168 MHz, or 198 MHz.Furthermore, it was observed that oscillation stopped when the copperplate was closely contacted to the electrode with sandwiching aninsulating member having the thickness of 3.17 mm.

Thus, if an inductor element simply made of one layer of electrode in aspiral shape is adopted and is formed on a copper plate, oscillatingoperation of an LC oscillator stops. This is because the inductance thatthe inductor element comprising one layer of electrode has becomes smallby making the copper plate approach the inductor element. The reason whythe inductance becomes small when the copper plate is made to approachthe inductor element maybe that eddy currents arise on a surface of thecopper plate owing to the magnetic flux generated when a signal isinputted into an electrode to cancel this magnetic flux.

FIG. 9 is a graph showing the measurement result of the outputcharacteristic in the case of configuring an LC oscillator with usingtwo layers of electrodes that have the same shape and arrangement as twoconductors 120 and 122 included in the inductor element 30 shown in FIG.2. In addition, FIG. 10 is a graph showing the output characteristic ofan LC oscillator in the case of closely contacting a copper plate to aninductor element having the same shape and arrangement as two conductors120 and 122 included in the inductor element 30.

The inductor element used for these measurements has the structure thatan electrode corresponding to the conductor 122 shown in FIG. 2 is addedto the inductor element shown in the measurement result in FIGS. 7 and8. In addition, if closely contacting the copper plate to this inductorelement, the lower electrode and copper plate are arranged through anadequate thin insulating member.

In the state of sufficiently separating an inductor element from otherconductive members, an LC oscillator using the inductor element wheretwo layers of spiral electrodes are located with facing each other hasan oscillation frequency near 70 MHz as seen from the measurement resultshown in FIG. 9. The reason why this oscillation frequency becomes lowerthan the oscillation frequency (119 MHz) at the time of using theinductor element comprising one layer of electrode shown in FIG. 7 isthat, since the inductor element comprising two layers of electrodesfunction as a compound element which has an inductance component and acapacitance component, this capacitance component lowers a resonantfrequency of the resonant circuit including the inductor element.

In addition, in a state of closely contacting the inductor elementhaving the electrode of two layers mentioned above to the copper plate,as shown in FIG. 10, a similar result appears although the position of aoscillation frequency (127 MHz) shifts. This shows that, by using theinductor element that has the double structure of the electrodesdescribed above, even if the inductor element is closely contacting tothe copper plate, the inductance component does not disappear and thefunction as an inductor conductor is maintained.

Thus, the inductor element made by forming two layers of electrodes in aspiral shape functions as an inductor conductor without the inductancecomponent disappearing even if a copper plate is closely contacted toone side (the electrode opposite to the electrode used as an inductorconductor) of them, and the oscillating operation of the LC oscillatorwhere this is used is maintained. Hence even if this inductor element 30and each configuration part of the LC oscillator 10 other than theinductor element 30 is formed on the semiconductor substrate 110, it ispossible to make the LC oscillator 10 perform oscillating operation byusing the inductor element 30 in this embodiment which has thefundamentally same structure.

Second Embodiment

FIG. 11 is a diagram showing the structure of an inductor element 30Aapplied for an LC oscillation in a second embodiment. The wholestructure of the LC oscillator in this embodiment is basically same asthe LC oscillator of the first embodiment shown in FIG. 1, and itsdetailed explanation is omitted. The inductor element 30A included inthe LC oscillator according to this embodiment is different in that apredetermined impedance element 200 is added to the inductor element 30in the first embodiment shown in FIG. 5. Namely, in the inductor element30 in the first embodiment described above, with paying attention to theother conductor 122 located so as to substantially superimpose the oneconductor 120 serving as an inductor conductor, only one end (the outercircumferential end in the example shown in FIG. 2) is connected to theconnecting wire 134 and the inner circumferential end is free (openstate). In this embodiment, the characteristics of the whole inductorelement 30A can be improved or adjusted by terminating the innercircumferential end of the conductor 122 through the impedance element200.

For example, when electric current flows into the one conductor 120 ofthe inductor element 30A, induced current flows to or electric currentdirectly flows through the connecting wire 134 into the other conductor122. However, it becomes possible to prevent unnecessary reflection inthis inner circumferential end by terminating the inner circumferentialend of the other conductor 122 through the impedance element 200. Inaddition, it becomes easy to improve or change the frequencycharacteristic of a circuit including the inductor element 30A byadjusting or changing a device constant of the impedance element 200.For example, what is necessary to make a frequency low is just to use aninductor as the impedance element 200. On the contrary, what isnecessary to make a frequency high is just to use a capacitor as theimpedance element 200. Alternatively, the impedance element 200 can beformed with arbitrarily combining these, that is, an inductor, acapacitor, and a resistor.

In addition, a chip part of an inductor, a capacitor, or a resistor canbe most easily used for the impedance element 200 described above. Inaddition, in consideration of forming two conductors 120 and 122, andthe like, which constitute the inductor element 30A, on thesemiconductor substrate 110 as shown by the cross-sectional structure inFIG. 6, it is desirable also to form the impedance element 200 on thesemiconductor substrate 110 with using semiconductor manufacturingtechnology. For example, what is conceivable is to form a resistor withusing a highly resistive material, to form a capacitor with making twolayers of metal layers, having predetermined areas, face each other, orto form an inductor with using conductors having predetermined shapes.In addition, since the impedance element 200 is used as an element fortermination, not-so-high Q is required even if this is realized with aninductor. For this reason, it also becomes possible to use an inductorconstituted by forming a conductor with a predetermined shape (forexample, a spiral shape) on the semiconductor substrate 110 as theimpedance element 200.

In addition, it is also good to use the impedance element 200 whosedevice constant can be changed by external control means. FIG. 12 is adiagram showing the structure in the case of connecting a variablecapacitance diode 210 to the inner circumferential end of the conductor122. The variable capacitance diode 210 operates as a capacitor withpredetermined capacitance by using it in a reverse biased state, whosecapacitance is changed by changing a reverse bias voltage. This variablecapacitance diode 210 is connected to the inner circumferential end ofthe conductor 122 through a capacitor 212 for DC component removal.

FIG. 13 is a drawing showing the cross-sectional structure in the caseof forming the variable capacitance diode 210, shown in FIG. 12, on thesemiconductor substrate 110. As shown in FIG. 13, a p+ region 220 formednear the surface of the semiconductor substrate 110 formed of an n typesilicon substrate (n-Si substrate) and an n+ region 222 further formedin a part thereof are included, and these p+ regions 220 and n+ region222 form a pn junction layer. In addition, an electrode 230 forgrounding is formed on the surface of the p+ region 220, and anelectrode 232 for applying an variable reverse bias voltage as a controlvoltage Vc is formed on the surface of the n+ region 222. By applyingthe positive control voltage Vc to the electrode 232, the variablecapacitance diode 210 whose capacitance changes according to theamplitude of this control voltage Vc can be formed.

FIG. 14 is a diagram showing the structure in the case of connecting avariable resistor, formed of an FET 240, to the inner circumferentialend of the conductor 122. As shown in FIG. 14, the variable resistanceis easily realizable by using a channel of the FET 240 as a resistor. Bychanging the control voltage Vc applied to a gate electrode, theresistance of the channel formed between a source and a drain can bechanged. In addition, the FET 240 can be easily formed on thesemiconductor substrate 110 by forming a source region and a drainregion near the surface of the semiconductor substrate 110, and formingelectrodes with predetermined shapes near regions in which the sourceand the drain and channels therebetween are formed.

Thus, it is possible to change termination conditions by terminating oneend of the conductor 122 with using an impedance element whose deviceconstant can be changed according to the control voltage Vc applied fromthe external. Hence, even if a frequency of a signal inputted into oroutputted from the inductor element 30A is changed, it is possible toadjust the termination conditions according to the change, and hence, toimprove characteristics of the LC oscillator.

The present invention is not limited to the above-described embodiments,but various types of modifications are possible within the scope of thegist of the present invention. For example, in the inductor element 30shown in FIG. 2, the inner end of the upper conductor 120 and the outerend of the lower conductor 122 are connected through the connecting wire134. Nevertheless, on the contrary, it can be also performed to mutuallyconnect the outer end of the upper conductor 120 and the inner end ofthe lower conductor 122. In addition, it can be also performed toconnect either outer ends or both inner ends of conductors 120 and 122when it is allowed that the inductance of an inductor element becomessmall to some extent.

FIG. 15 is a graph showing the measurement result of the outputcharacteristic in the case of configuring an LC oscillator with using aninductor element that has two layers of electrodes in the same shape andarrangement as two conductors 120 and 122 included in the inductorelement 30 shown in FIG. 2 and in which each outer circumferential endof the two electrodes is mutually connected. In addition, FIG. 16 is agraph showing the measurement result of the output characteristic of theLC oscillator at the time of closely contacting the copper plate to theinductor element used for the characteristic measurement shown in FIG.15. In addition, these measurement results come from the experimentalresults included in the application described above (Japanese PatentApplication No. H10-140541) as it is. As shown in these figures, in theLC oscillator where the inductor element in which both outercircumferential ends of two electrodes are mutually connected is used,its oscillation frequency changes from 117 MHz to 171 MHz by closelycontacting the copper plate. Nevertheless, oscillating operation ismaintained without stopping.

In addition, since two conductors 120 and 122 included in the inductorelements 30, 30A are formed in spiral shapes in the embodimentsdescribed above, it is possible to realize the inductor elements 30, 30Ahaving large inductance.

Nevertheless, it is also good to form two conductors 120 and 122 inmeander shapes (FIG. 17A) In addition, the inductance of the inductorelements 30, 30A can be small when they are used as one part of a highfrequency circuit. Hence it is also good to form the inductor elements30, 30A less than one turn by reducing the numbers of turns of theconductors 120 and 122 (FIG. 17B), or to form them in an substantiallylinear shape (FIG. 17C).

In addition, although the shapes of two conductors 120 and 122 are setsubstantially similarly in the embodiments described above, it is alsogood to set them in different shapes. For example, it can be alsoperformed to set the number of turns of the lower conductor 122 to bemore than that of the upper conductor 120. Thus, since the upperconductor 120 does not directly face the semiconductor substrate 110 ifall or part of the lower conductor 122 is arranged under the upperconductor 120, it is possible to effectively prevent the generation ofeddy currents due to the upper conductor 120.

In addition, although the inductor elements 30, 30A are formed byforming two conductors 120 and 122 on the semiconductor substrate 110 inthe embodiments described above, the inductor element in which twoconductors 120 and 122 are formed on a conductor substrate such as ametal is also realizable. From the experimental result shown in FIG. 10,it is confirmed that, even in this case, this effectively functions asthe inductor element and that the LC oscillator performs oscillating. Ifit becomes possible to form the inductor elements 30, 30A by closelycontacting them on a conductor substrate, it also becomes possible toarrange the inductor elements 30, 30A on a front side of a metalshielding case or the like. Hence it becomes easy to secure aninstallation space of the inductor element.

In addition, in the inductor elements 30 and 30A in respectiveembodiments described above, each connecting wire 134 different from thelead wires 130 and 132 is used for mutually connecting both odd ends ofthe two conductors 120 and 122. Nevertheless, as shown in FIG. 18, it isalso good to mutually connect both odd ends of the two conductors 120and 122 with using a part of one lead wire 132. In this case, theconnecting wire 134 becomes unnecessary. Hence it becomes possible tosimplify structure, and further, to improve characteristics since it isprevented that unnecessary magnetic flux by the connecting wire 134 isgenerated, and that effective magnetic flux generated by the inductorconductor is disturbed.

Furthermore, although a Clapp circuit is used as an LC oscillator in theembodiments described above, it is also good to use another LCoscillator such as a Colpitts circuit that makes oscillating operation,where the resonance of an inductor and a capacitor is used, performed.Even in this case, by using an inductor element having the structureshown in FIG. 2 etc. as an inductor element included in the LCoscillator, it is possible to realize an LC oscillator which performsoscillating operation on a semiconductor substrate or a conductorsubstrate.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, a conductor thatis one of two conductors, both odd ends of which are mutually connected,and is apart from a substrate is used as an inductor conductor, and alead wire of this inductor conductor passes between another conductor,being near to the substrate, and the substrate. Hence it is possible tosuppress to the minimum the interruption of the flow of effectivemagnetic flux generated by the inductor conductor. Therefore, with usingthis inductor element as a part of an LC oscillator, the LC oscillatorthat is having good characteristics can be formed on the substrate, andoscillation can be performed.

In addition, according to the present invention, electric current flowsalso to another conductor by effective magnetic flux generated by theinductor conductor. Nevertheless, by terminating the free end of thisother conductor by an impedance element, it becomes possible to preventunnecessary reflection in this portion, and hence, to improvecharacteristics of the inductor element. Therefore, it is possible toform an LC oscillator having further good characteristics on asubstrate.

What is claimed is:
 1. An LC oscillator using an inductor element formedon a substrate, characterized in that the inductor element has twoconductors that are formed in piles on the substrate in the state wherethey are mutually insulated, and are connected at both odd ends, andwherein one of the conductors apart from the substrate is used as aninductor conductor, and a lead wire of this inductor conductor islocated so as to pass between another one of the conductors, being nearthe substrate, and the substrate.
 2. The LC oscillator according toclaim 1, characterized in at that in the inductor element the twoconductors and the lead wire are formed respectively with using metallayers, which are different layers being mutually apart by one or morelayers, in the three or more layers of metal layers that are formed onthe substrate.
 3. The LC oscillator according to claim 1, characterizedin that the inductor element mutually connects both odd ends of the twoconductors with using a part of the lead wire.
 4. The LC oscillatoraccording to claim 1, characterized in that the substrate is asemiconductor substrate, and components are formed on the substrate inwhich the inductor element is formed.
 5. The LC oscillator according toclaim 1, characterized in that the two conductors have substantially thesame shape.
 6. The LC oscillator according to claim 1, characterized inthat the two conductors have long shapes, and one end of one conductorin a longitudinal direction is connected with one end of the other inthe longitudinal direction.
 7. The LC oscillator according to claim 1,characterized in that the two conductors have circular shapes less thanone turn, and one end of one conductor is connected with one end of theother.
 8. The LC oscillator according to claim 1, characterized in thatthe two conductors have spiral shapes each number of turns of which isone or more, and one end of one conductor is connected with one end ofthe other.
 9. The LC oscillator according to claim 1, characterized inthat the two conductors each have a spiral shape of one or more turns,mutually connect both odd ends, and also makes the lead wire, led outfrom the inner circumferential end of the inductor conductor, passbetween the other conductor and the substrate.
 10. The LC oscillatoraccording to claim 1, characterized in that the two conductors areformed in substantially linear shapes, and one end of one conductor isconnected with one end of the other.
 11. The LC oscillator according toclaim 1, characterized in that the two conductors are formed in meandershapes, and one end of one conductor is connected with one end of theother.
 12. The LC oscillator according to claim 8, characterized in thatan inner end of said one conductor is connected with an outer end of theother conductor.
 13. The LC oscillator according to claim 1,characterized in that the inductor element has an inductance componentof the conductor of an upper layer, and a capacitance component betweenthe two conductors.
 14. An LC oscillator using an inductor elementformed on a substrate, characterized in that the inductor element hastwo conductors that are formed in piles on the substrate in the statewhere they are mutually insulated, and are mutually connected at bothodd ends, and wherein one of the conductors apart from the substrate isused as an inductor conductor, and further, an end that is an end ofanother one of the conductors and is not connected to the inductorconductor is terminated with a predetermined impedance element.
 15. TheLC oscillator according to claim 14, characterized in that it ispossible to change at least one device constant of a resistor, acapacitor,and an inductor in the impedance element, and terminationconditions are changed by making the device constant variable.
 16. TheLC oscillator according to claim 15, characterized in that the substrateis a semiconductor substrate, and the capacitor is formed of a variablecapacitance diode made of a semiconductor layer formed in the inside oroutside of the semiconductor substrate.
 17. The LC oscillator accordingto claim 15, characterized in that the substrate is a semiconductorsubstrate, and the resistor is formed of a channel of an FET made of asemiconductor layer formed in the inside or outside of the semiconductorsubstrate.
 18. The LC oscillator according to claim 14, characterized inthat the substrate is a semiconductor substrate, and components areformed on the substrate in which the inductor element is formed.
 19. TheLC oscillator according to claim 14, characterized in that the twoconductors have substantially the same shape.
 20. The LC oscillatoraccording to claim 14, characterized in that the two conductors havelong shapes, and one end of one conductor in a longitudinal direction isconnected with one end of the other in the longitudinal direction. 21.The LC oscillator according to claim 14, characterized in that the twoconductors have circular shapes less than one turn, and one end of oneconductor is connected with one end of the other.
 22. The LC oscillatoraccording to claim 14, characterized in that the two conductors havespiral shapes each number of turns of which is one or more, and one endof one conductor is connected with one end of the other.
 23. The LCoscillator according to claim 14, characterized in that the twoconductors are formed in substantially linear shapes, and one end of oneconductor is connected with one end of the other.
 24. The LC oscillatoraccording to claim 14, characterized in that the two conductors areformed in meander shapes, and one end of one conductor is connected withone end of the other.
 25. The LC oscillator according to claim 22,characterized in that an inner end of said one conductor is connectedwith an outer end of the other conductor.
 26. The LC oscillatoraccording to claim 14, characterized in that the inductor element has aninductance component of the conductor of an upper layer, and acapacitance component between the two conductors.